This application claims the priority of Japanese Patent Application No. 10-54422 filed on Feb. 18, 1998, Nos. 10-55937 and 10-55938 and 10-55939 filed on Feb. 20, 1998, No. 10-96784 filed on Mar. 25, 1998 which are incorporated herein by reference.
The present invention relates to an electronic-endoscope light quantity controlling apparatus, and in particular, to the contents of light quantity control for adjusting the light quantity when a still image is selected using an electronic-endoscope that uses the conventional image mix reading system to form a moving image and that reads out all pixels accumulated in an image pickup device to form a still image.
In an electronic-endoscope apparatus, for example, CCD (Charge Coupled Device) is used as a solid image-pickup device, and this CCD is structured so as to obtain an image signal (video signal) by reading out charge accumulated in units of pixels by a photoelectric conversion device. In, for example, a simultaneous type electronic-endoscope apparatus, color filters are arranged in units of pixels on the top surface of the forgoing CCD to thereby obtain a color image.
FIG. 21 shows an arrangement state for the forgoing color filters, and Mg (magenta) and Cy (cyan) pixels are arranged on, for example, an even line, and G (green) and Ye (yellow) pixels are arranged on an odd line on a picked-up surface of CCD1 as shown. In this CCD1, accumulated charge (pixel signal) in units of pixels is to be obtained through these color filters.
According to a conventional color difference line sequential mix reading (pixel mix reading) system, accumulated charges of pixels on the upper and lower lines are added and mixed to be readout. For example, during first exposure, video signals of such odd field as a mixed signal of 0-line and 1-line, a mixed signal of 2-line and 3-line, . . . are read out, and during the second exposure, video signals of such even field as a mixed signals of 1-line and 2-line, a mixed signal of 3-line and 4-line, . . . are read out. Therefore, two lines of mixed signals of CCD1 become one line of signals of field image, and one odd or even field of data are to be obtained by one exposure.
FIG. 22 shows an operation of signals read out from the foregoing CCD1, and in an electronic-endoscope apparatus, an odd field and an even field are formed on the basis of the O (Odd)/E (Even) signal (field signal) for each {fraction (1/60)} second (vertical synchronizing period) as shown in FIG. 22(A). Therefore, as shown in FIG. 22(B), signals are accumulated in accumulation (exposure) time T of an electronic shutter during the forgoing period of {fraction (1/60)} second, and the accumulation mixed signal is read out during the next {fraction (1/60)} second period. As a result, as shown in FIG. 22(c), an odd field signal, and an even field signal are to be obtained, and for example, the (nxe2x88x921)th odd field signal becomes mixed signals of (0+1) line, (2+3) line, (4+5) line . . . which are shown on the left of FIG. 21, and the n-th even field signal becomes mixed signals of (1+2) line, (3+4) line, . . . which are shown on the right of FIG. 21.
These odd field signals and even field signals are interlace scanned to be formed as a one-frame image, and this image is displayed as a moving image on a monitor. Also, in the endoscope apparatus, a freeze switch is arranged in the operating unit, and when this freeze switch is depressed, a still image at the time is formed and displayed.
In the foregoing simultaneous type electronic-endoscope apparatus, however, there is a time lag of {fraction (1/60)} second between those odd field image and even field image which are used to form the one-frame image as shown in the foregoing FIG. 22(C), and if there is a shake of the endoscope itself, a movement of the object to be observed or the like during this period of time, there is the problem that the image quality (resolution, color shift, etc.) will be deteriorated when the still image is displayed. In other words, in the case of a moving image, it is often better to faithfully reproduce the movement and the like of the subject conversely by the foregoing mix reading system in the CCD1, but in the case of a still image, the resolution will be deteriorated.
Thus, the applicant sets a predetermined light shielding period and uses an all-pixel reading system for reading all pixels out from data obtained during one exposure using this period. However, due to a delay in a mechanical (gear) response from, for example, a light shielding plate that sets the light shielding period, the exposure may be insufficient during the period of time required to read out all pixels. That is, complete light shielding conditions are required during the light shielding period required to read out data, so the light shielding plate is activated slightly before the beginning of the light shielding period in view of its response time. This response operation (the operation performed until complete light shielding is achieved) may cause lack of light quantity.
The present invention has been achieved in the light of this problem, and its object is to provide an electric-endoscope light quantity controlling apparatus that can compensates for the lack of light quantity caused by delayed responses from a light shielding mechanism in an electronic-endoscope adapted to obtain a high-quality image using the light shielding period.
In order to achieve this object, this invention is characterized by comprising a driving circuit for driving an all-image reading system that reads out signals for all pixels accumulated on an image pickup device during a single exposure, light shielding means for intercepting light for a predetermined period of time in order to allow all pixels to be read out when the all-pixel reading system is selected, and light quantity compensating means for compensating for lack of light quantity caused by a delayed response from the light shielding means for a light shielding operation.
The light quantity compensating means may comprise light quantity controlling means for adjusting the outgoing light quantity from a light source during a period immediately before light shielding. The light quantity controlling means may variably control the lamp voltage or the aperture of a light quantity restrictor.
According to this configuration, for example, a freeze switch can be depressed to form a still image using the all-pixel reading system. In the all-pixel reading system, during a predetermined (the first) period of {fraction (1/60)} second (a vertical synchronizing period), charges are accumulated due to exposure (the exposure time is arbitrary), and during the second period (in the next exposure), the odd lines in the image pickup device (CCD) are read out and stored in a predetermined memory. During the third period ({fraction (1/60)} second), the remaining even lines are read out and stored in a predetermined memory. To allow the even lines to be read out, the light shielding means intercepts light from a light source during the second period.
That is, if, during the second period during which accumulated charges in the odd lines are sequentially readout, subsequent charges are accumulated, as in the prior art, the remaining even lines cannot be read out. Thus, this invention eliminates the optical output during the second period and reads out the accumulated charges in the even lines during the third period. Thereby, the signals of all pixels of the image pickup device obtained by a single exposure can be read out.
Next, for example, video signals for the odd lines stored first in the memory are stored in a phase adjustment memory and are delayed by {fraction (1/60)} second, and a mixing circuit then executes pixel mix processing between data for the odd and even lines. This pixel mix processing forms signals equivalent to those obtained by a pixel mix reading system operating when the image pickup device outputs signals, but is distinguished from this system in that it mixes pixels based on data obtained during a single exposure.
Pixel mix signals are used to form odd and even field signals, and a still image is displayed based on these video signals. Thus, the still image is formed based on the signals for all pixels obtained during the single exposure and has a high quality.
On the other hand, in a normal condition under which the freeze switch is not pressed, the pixel mix reading system operating when the image pickup device outputs has been selected, and pixels in two lines read out from the image pickup device as in the prior art are mixed together and output to provide a moving image that reproduces motions of an object faithfully.
In the light shielding operation for still images, however, the light quantity may become insufficient during the exposure period for still-image formation due to a delayed mechanical response from the light shielding plate, as described above. Thus, the light quantity controlling means according to this invention supplies a higher lamp lighting voltage than that of usual to the light source during the exposure for still-image formation to provide an appropriate light quantity, thereby enabling an appropriately bright still image. In addition, adjusting the diaphragm aperture enables an appropriate light quantity to be obtained.
Another aspect of this invention is characterized by comprising as the light quantity compensating means, amplifying means for amplifying an image signal output from the image pickup device by an amount corresponding to the shortage of light quantity. If the amplifying means comprises a digital signal processing circuit for converting an image signal output from the image pickup device into a digital signal for various digital processing including gamma correction, an amplifier may be provided in an analog-signal processing area located before or after the digital signal processing circuit.
According to this aspect, the amplifier amplifies an image signal output from the image pickup device by an amount corresponding to the shortage of light quantity to provide an appropriate light quantity, thereby enabling an appropriately bright still image to be displayed.
The amplifying means may comprise an arithmetic circuit provided in a digital signal area that processes image signals digitally, in order to multiply a digital image signal by an amount corresponding to the lack of light quantity caused by a delayed response from the light shielding means for a light shielding operation. Accordingly, also in the digital signal area, the lack of light quantity caused by the delayed response of a light shielding mechanism can be compensated by a multiplier.
Another aspect of this invention is characterized in that the apparatus comprises an electronic shutter circuit for controlling as a shutter time the time during which charges are accumulated in the image pickup device, and in that the amplifying means comprises an amplifier for amplifying an image signal output from the image pickup device by an amount corresponding to the lack of light quantity caused by a delay in a response form the light shielding means for a light shielding operation, using a gain corresponding to the shutter time set by the electronic shutter circuit.
Some electronic-endoscopes apparatus use an electronic shutter function, wherein the effect of the insufficient light quantity caused by a delayed mechanical response from the light shielding plate increases with decreasing shutter time, thereby forming an unstably bright still image. Thus, this invention uses the amplifier to amplify signals using a gain corresponding to the shutter time, that is, using a larger gain for a shorter shutter time, thereby providing an appropriate light quantity.
Another aspect of this invention is characterized by including as the light quantity compensating means an electronic shutter means for the charge accumulation time for the image pickup device during a period immediately before light shielding. According to this aspect, the electronic shutter means can, for example, control the exposure time for still images to be longer than that for moving images, thereby providing an appropriate light quantity to enable an appropriately bright still image to be displayed.
Yet another aspect of this invention is characterized by applying the invention of the all-pixel reading system to an electronic-endoscope and forming a moving image using a pixel mix reading system at the output of the image pickup device that mixes together and outputs vertically arranged lines of image signals accumulated in the image pickup device, while forming a still image using the all-pixel reading system that uses the light shielding period to read out signals for all pixels accumulated in the image pickup device during a single exposure period.